Actuators used for work, such as conveyance of a workpiece, or a chucking operation, a working operation, or the like for the workpiece is operated by energy, such as an air pressure, a liquid pressure, electricity, and so forth. In the above-described actuators, although an electric actuator utilizing electric energy is advantageous at a point that a movement position thereof can be freely changed or adjusted, the structure thereof is complicated and specifically, in the electric actuator having a construction to obtain a linear movement, the structure thereof is further complicated. Furthermore, when large force of application is attempted to be obtained, growing in size of the actuator, and growing in electric power consumption thereof cannot be avoided. Hence, in a case that a constant stopping position of the actuator is retained, the electric power has to be continuously supplied in the meantime, and therefore a loss in view of energy saving is also large. Moreover, in a case that the force of application is added to a load via a rod or the like, not only a mechanical loss tends to be caused by that a power transmitting portion of the actuator directly receives an impact, but also there is a possibility that excessive repulsive force is applied to the load.
On the other hand, as an actuator utilizing the air, an air cylinder is well known. This air cylinder is that for converting energy of compressed air into a linear movement. There are a double-action air cylinder that is moving a piston by means of alternately supplying air into a pressure chamber at each of both sides of the piston, and a single-acting air cylinder that is moving a piston by means of air supplied to and discharged from a pressure chamber at one side of the piston and a spring force of a spring installed at the other side of the piston. Since in any one of these types of the air cylinders, the linear movement can easily be obtained in comparison with the electric actuator, the same is widely utilized for various operations.
However, in the air cylinders, ordinarily, a moving stroke of the piston is mechanically determined and the piston is configured to move between a position at an advancing end and a position at a retreating end that are regulated by a stopper or the like. Consequently, it is difficult to change or adjust the moving stroke (movement position) of the piston. Specifically, it is difficult to arbitrarily change or adjust the moving stroke of the piston. Hence, it is general to selectively use the air cylinders each having different moving strokes, corresponding to the work.